The present invention relates to therapeutic uses of bactericidal/permeability-increasing (BPI) protein products for the treatment of adverse physiological effects associated with intestinal ischemia/reperfusion.
Reperfusion of ischemic intestines is associated with profound cardiovascular and respiratory dysfunction that may lead to shock and death. A variety of mediators are believed to be released from the ischemic tissue that could lead to cardiorespiratory collapse, including oxygen free radicals, protanoids, and platelet activating factor.
During ischemia, breakdown of the intestinal mucosal permeability barrier may result in translocation of endotoxin and/or bacteria from the intestinal lumen. Endotoxin has been detected in the portal vein after intestinal ischemia/reperfusion. However, a role for translocated bacteria or endotoxin in intestinal ischemia/reperfusion injury has not been clearly defined.
Bactericidal/permeability-increasing protein (BPI) is a protein isolated from the granules of mammalian PMNs, which are blood cells essential in the defense against invading microorganisms. Human BPI protein has been isolated from polymorphonuclear neutrophils by acid extraction combined with either ion exchange chromatography [Elsbach, J. Biol. Chem., 254:11000 (1979)] or E. coli affinity chromatography [Weiss, et al., Blood, 69:652 (1987)] referred to herein as natural BPI and has potent bactericidal activity against a broad spectrum of gram-negative bacteria. The molecular weight of human BPI is approximately 55,000 daltons (55 kD). The amino acid sequence of the entire human BPI protein, as well as the DNA encoding the protein, have been elucidated in FIG. 1 of Gray et al., J. Biol. Chem., 264:9505 (1989), incorporated herein by reference.
The bactericidal effect of BPI has been shown to be highly specific to sensitive gram-negative species, while non-toxic for other microorganisms and for eukaryotic cells. The precise mechanism by which BPI kills bacteria is as yet unknown, but it is known that BPI must first attach to the surface of susceptible gram-negative bacteria. This initial binding of BPI to the bacteria involves electrostatic interactions between the basic BPI protein and the negatively charged sites on lipopolysaccharides (LPS). LPS has been referred to as "endotoxin" because of the potent inflammatory response that it stimulates. LPS induces the release of mediators by host inflammatory cells which may ultimately result in irreversible endotoxic shock. BPI binds to Lipid A, the most toxic and most biologically active component of LPS.
In susceptible bacteria, BPI binding is thought to disrupt LPS structure, leading to activation of bacterial enzymes that degrade phospholipids and peptidoglycans, altering the permeability of the cell's outer membrane, and ultimately causing cell death by an as yet unknown mechanism. BPI is also capable of neutralizing the endotoxic properties of LPS to which it binds. Because of its gram-negative bactericidal properties and its ability to neutralize LPS, BPI can be utilized for the treatment of mammals suffering from diseases caused by gram-negative bacteria, such as bacteremia or sepsis. Bahrami et al., Int'l Endotoxin Soc. Meeting, Vienna, Austria (August 1992), disclose the use of a BPI protein for the treatment of hemorrhagic shock.
A proteolytic fragment corresponding to the N-terminal portion of human BPI holoprotein possesses the antibacterial efficacy of the naturally-derived 55 kD human holoprotein. In contrast to the N-terminal portion, the C-terminal region of the isolated human BPI protein displays only slightly detectable anti-bacterial activity. Ooi, et al., J. Exp. Med., 174:649 (1991). A BPI N-terminal fragment, comprising approximately the first 199 amino acid residues of the human BPI holoprotein and referred to as "rBPI.sub.23 ", has been produced by recombinant means as a 23 kD protein. Gazzano-Santoro et al., Infect. Immun. 60:4754-4761 (1992).